This invention relates to methods and apparatus for the detection and identification of volatile materials, especially odors. For the purposes of the present specification, an odor is a material in a gaseous or volatile state either in a native, gaseous condition or in a form which has been given off or released by a solid or a liquid. Many such odorous, volatile materials are detectable by sensation by one or more animals, especially mammals, including humans. For convenience, however, odors, as contemplated by the present invention, include not only those volatile materials which are capable of being sensed by humans or other mammals but also those which are capable of being detected through the employment of one or more embodiments of the present invention.
Numerous methods have been proposed for the detection of odor. See in this regard, "Modern Theories of Odor and Olfaction and Objective Olfactometry", Tanyolac, Excerpta Medica, International Congress Series No. 206-OTO-RHINO-LARYNGOLOGY; Proceedings of the 9th International Congress, Mexico D.F., Aug. 10-14, 1969. Thus, it has been known to employ thermal, colorimetric determinations for the detections of certain toxic leaks. A "stinkometer" was developed in 1945 comprising a wet chemical colorimetric determination for determining the putrefaction of fish. Additionally, on Odocell developed in 1949, has also been employed to detect odor. The Odocell used the effect of odor-containing air on the surface tension of liquids to determine the presence and characteristics of odors.
As further reported in the proceedings in the 9th International Congress paper by Tanyolac, an electrochemical means for the determination of odors employing an electrolytic solution has also been reported as has a contact-potential olfactometer based upon the change of contact potential along various solid surfaces.
Yet another attempt at detection of odor has relied upon the changes in temperature of a film due to adsorption of odorous vapors thereupon. A thermistor coated with certain films is used as a sensing element for detecting such changes in temperature.
A further prior approach to the detection of odor is the Electro-Odocell. This device and method is reported, for example, in Great Britain Pat. No. 1,105,641 dated Mar. 6, 1968 in the name of Tanyolac and Gultekin, together with foreign language counterparts thereof including Swiss Pat. No. 499,106 and West German Pat. No. 1,673,104. This Electro-Odocell is also reported in the proceedings of the 9th International Congress paper referred to previously. It is also discussed in "The Electro-Odocell for Odor Measurement and Surface Effects", Tanyolac, Surface Effects in Detection, pp. 89-100, Spartan Books (1965); "Electro-Odocell and Theories of Odor", Tanyolac, Theories of Odor and Odor Measurement, pp. 537-561, Technivision (1968); and "The Electro-Odocell for Inspection and Grading of Meat and Fish", Tanyolac, Olfaction and Taste II, Proceedings of the 2nd International Symposium, Tokyo, September, 1965, pp. 609-623, Pergamon Press (1967).
The static Electro-Odocell provides for the static detection of odor by exposing a dielectric material to odor molecules and detecting the resulting changes in surface potential as adsorption of the molecules occurs. The maximum value of surface potential is related to adsorption of the maximal amount of odor molecules, taken in sum, on the dielectric sensor. While an initial transient, representing a value of approximately 10% of the final potential, may be detected within a few seconds, the final values require substantially longer to ascertain. This static Electro-Odocell is cumbersome to employ and requires a lengthy period of purging of odor molecules from the dielectric surface between uses.